I. Field of the Invention
The present invention relates generally to the reduction of greenhouse gases in the atmosphere and, more particularly, to the capture and sequestration of carbon dioxide from a variety of sources such as gases from uses involving carbon combustion, a principal source being flue gases, including, without limitation, those from cement plants, fossil fuel fired power plants, and other industrial commercial and domestic emissions. The invention features alkali metal carbonate scrubbing followed by reaction with a metal oxide or metal carbonate to form a salt containing the carbon dioxide in stable form or other sequestering use of carbon dioxide to reduce undesirable effects caused by carbon dioxide released to the atmosphere.
II. Related Art
Carbon dioxide has long been a by-product of many industrial processes. Large amounts of carbon dioxide are released to the atmosphere, for example, by power plants burning carbonaceous fuels, including coal and petroleum products and by Portland cement plants where fossil fuels are burned and CO2 is released in large amount from the calcining of limestone. This generation of large amounts of carbon dioxide was of little or no concern until recently when the participation of carbon dioxide in the accumulation of greenhouse gases and the possible affect this may have on global warming was recognized. It has since become a concern of some urgency such that there exists a definite need to reduce the amount of carbon dioxide released to the atmosphere by combustion processes and coal and petroleum fired electric power plants and plants producing Portland cement have been singled out as examples of process which release vast amounts of CO2 per year.
In response to the rising concern regarding CO2 emissions, techniques and systems have been proposed to reduce CO2 emissions by removal of CO2 from flue gases using a variety of approaches. For example, U.S. Pat. No. 6,655,150 proposes a chemical absorption and desorption process for a power and/or heat generation plant in which the plant exhaust gas is fed to an absorber where CO2 is absorbed using a chemical absorbent leaving a CO2 depleted exhaust gas stream. The CO2 is removed from the absorbent in a desorber and the COs is discharged to other uses. That system requires heating, cooling and pressurized vessels and is rather complicated. Another approach is found in U.S. Pat. No. 6,648,949 which discloses a flue stack application for CO2 and particle removal which uses the stack as a biological reactor to promote a photo-synthesis reaction between carbon dioxide and algae-laden water to form carbohydrate products for carbon dioxide sequestration. In U.S. Pat. No. 6,908,507, carbon dioxide is captured in solution using a biologically derived catalyst to hydrate it to carbonate and bicarbonate ions. The catalyst is an enzyme such as carbonic anhydrase, for example. The dissolved carbonate and bicarbonate are then reacted with dissolved metal ions (preferably dissolved lime) to precipitate a stable carbonate, nominally calcium carbonate. While such a approach might be successful, it is noted that it would be quite expensive to provide the enzyme in the quantities required.
Presently, there remains a definite need for the provision of a practical and cost-effective process to remove carbon dioxide from flue gases which can readily be implemented.